Kono Yo no Hate de Koi wo Utau Shoujo Yu-no

Yu-no. A Girl Who Chants Love at the Bound of this World.

この世の果てで恋を唄う少女YU-NO

Takuya Arima is a young student whose father, a historian who has conducted various investigations, disappeared recently. During a summer vacation, Takuya receives a peculiar package from his missing father, along with a letter containing information about the existence of various parallel worlds. At first, Takuya doesn't take it seriously, but soon he realizes that he possesses a device that allows him to travel to alternate dimensions. Is his father alive, after all? If so, where is he?